Five degrees BTDC is insufficient with today's fuel. Try increasing the timing with the octane selector until the stumble goes away. That stumble is more ofen insufficient advance than a carb issue. I'd be willing to bet that the stumble will go away at between 7 and 10 degrees more advance on the octane selector. You will, of course, have to back it off if you get pinging under load or bucking against the starter.
